1. Field of the Invention
This invention relates to the field of treatment of crease-resistant fabrics and in particular to the reduction of the free formaldehyde contents thereof.
2. Description of the Prior Art
The finishing of cellulosic fabrics to impart wash, wear and so-called durable press properties to them usually consists in the application and reaction of an agent on the fabric. Such agents normally react to form chemical bonds or crosslinks between the long linear cellulose molecules. The agents most commonly used for these finishing techniques are methylol amides formed by the addition of formaldehyde to organic compounds of the amide class. Since the formaldehyde forms the methylol group that reacts with the cellulose and since the methylol compound must react with more than one group appendant to the cellulose for the treatment to be effective, the average molar ratio of added formaldehyde to amide compound must be greater than 1. Quite commonly, the agents used are dimethylol compounds, such as, N,N'-dimethylolethylene urea, N,N'-dimethylolurea, N,N-dimethylolethyl carbamate, N,N'-dimethylol dihydroxyethylene urea, N,N'-dimethylol triazone or methylolated melamine where the degree of methylolation ranges from 3 to 6. The etherified versions of these resins are also suitable, e.g., N,N'-dimethoxymethyl ethylene urea.
Other types of agent are also suitable for use to render fabrics crease-resistant, but in each case, they involve some type of formaldehyde derivative. Such agents ultimately have one undesirable property in common, namely, the release of formaldehyde, as those methylol groups which have not reacted with the cellulose decompose on the fabric. This occurs slowly as atmospheric moisture or laundering hydrolyzes the unreacted methylol groups. It is virtually impossible to obtain 100% reaction of the methylol groups with the fabric. Since formaldehyde is irritating even at low concentrations, fumes from fabric containing unreacted agent can be very objectionable.
Numerous attempts have been made to reduce the amount of formaldehyde in such durable press agents. Generally, these have taken the form of creating new agents which did not release as much formaldehyde. Typical of these attempts are the inventions disclosed in U.S. Pat. No. 3,755,418 and U.S. Pat. No. 3,749,751. See also U.S. Pat. No. 3,597,380.
Methods for the reduction of the formaldehyde odor wherein the fabrics are treated with certain types of scavenging agents are also known. See, for example, U.S. Pat. Nos. 3,723,058 and 3,590,100. See also U.S. Pat. No. 3,723,377.
Typically, however, inasmuch as these processes are generally carried out using the appropriate scavenging agent either dissolved or dispersed in a liquid medium, e.g., water or an organic solvent, relatively large amounts of liquid medium must be removed from the fabric during the drying operation. Consequently, a substantial amount of the cost incurred in the process resides in the liquid medium removal step.
Such liquid media present a further problem in that after they are removed, they must either be disposed of or recovered for reuse. In the case of an aqueous treatment system wherein the liquid medium is water, the water is normally disposed of as waste. In recent years, the environmental problems that relate to the disposal of water with residual chemical agents therein have become increasingly important.
With respect to organic solvents as the liquid medium, it is normally desirable to recover them because of the relatively high cost. Obviously, such recovery systems only add to the expense of the overall treatment process. Moreover, disposal of the solvent, if it is desired not to recover it, also presents environmental problems.
The foregoing problems become even more severe when textile fabrics which are highly absorbent are treated. Additionally, because of the relatively large absorption of the liquid, the weight of the wet fabric which is being handled increases significantly, and often results in processing problems and increased expense.
Methods have been developed wherein types of treating agents, e.g., dyes, and the like, can be applied to fabrics in the form of a foam. Such methods are directed to avoidance of the problems outlined above in connection with liquid removal. In particular, reference is made to U.S. Pat. Nos. 4,118,526, 4,193,762, 4,208,173, 4,266,976, 4,270,915, 4,282,729, and 4,299,591, the contents of each of which are hereby incorporated by reference.